1. Field of the Invention
This invention relates generally to concrete crack repair and more specifically to concrete internal metal stitching and a cost effective method for restoring the tensile strength to a cracked concrete section.
2. Description of the Prior Art
Concrete stitching is a simple, cost effective technique for restoring the tensile strength to a cracked concrete section. It also can increase the shear capacity of flexural members. Most repair contractors already have the necessary equipment and tools to stitch cracks.
The most common stitching methods use either stitching dogs (U-shaped metal units) thin metal interlocking plates, or dowel bars for reinforcement. In each method, the reinforcement is installed across the crack and is bonded to each side of the crack with epoxy or cementitious materials. The amount of reinforcement can be varied to achieve the desired strength restoration. Unlike interlocking plates and dowel bars, which are embedded in the concrete, stitching dogs are surface mounted. Concrete in axial tension, therefore, stitching dogs on both faces. Stitching dogs are most effective when restoring tension in bending members since they are placed at the critical location-the tension face.
To install stitching dogs, holes are drilled on both sides of the crack, the holes are cleaned, and the legs of the dog are anchored in the holes with nonshrink grout or epoxy. The length, orientation, and location of the stitching dogs are varied so that the tension is transmitted across the area, not across a single plane within the section.
Because dogs are thin and long and aren't supported laterally, they cannot take much compressive force. If the crack closes as well as opens, the dogs must be stiffened and strengthened to prevent buckling. One method to prevent buckling is to embed the dogs in an overlay.
Dowel bars are also used to repair concrete cracks. To install dowel bars, two holes are drilled diagonally through the crack, one from each side. The holes are filled with nonshrink cementitious or epoxy materials, then a dowel bar is driven into each hole. The bonded dowel bars transmit force across the crack face. The angled dowel bars restore shear transfer and transmit axial tension, but aren't very effective for restoring tension in flexural members.
Because dogs are thin and long, and aren't supported laterally, they cannot take much compressive force. If the crack closes as well as opens, the dogs must be stiffened and strengthened to prevent buckling. The angled dowel bars restore shear transfer and transfer axial tension, but aren't very effective for restoring tension in flexural members.